1. Field of the Invention
This invention relates to a fuel feeder for feeding liquid fuel from a fuel tank to an automotive engine and, more particularly, to a fuel feeder for an automotive engine, in which fuel is supplied from a sub-tank provided in the fuel tank.
2. Description of the Related Art
When a vehicle is suddenly accelerated or decelerated or when it suddenly turns, a great momentum is exerted to it in a longitudinal or transversal direction. In addition, when the vehicle runs along a slope, a gravitational force acts on the vehicle in longitudinal and transversal directions. In such situations, the liquid fuel contained in the fuel tank is forcibly brought to one side thereof. In such case, the effective head or liquid level in the fuel tank is lowered, and it is possible that the withdrawal port of a fuel pump which is disposed in the fuel tank is brought to be aloof from the liquid level. With the occurrence of the lack of fuel around the fuel pump withdrawal port, the fuel pump sucks air, thus reducing the pressure of fuel fed from the pump, that is, generating a phenomenon of engine breathing.
Accordingly, it has been thought to dispose a sub-tank on the bottom of the fuel tank and locate the fuel pump withdrawal port in the sub-tank, as shown in U.S. Pat. No. 4,397,333. In such a fuel feeder, withdrawal of fuel in the fuel tank into the sub-tank is caused by a jet of excess fuel which is returned from the engine to the fuel tank. With this fuel feeder, a sufficiently high liquid level can be held in the sub-tank even when the liquid level in the fuel tank is reduced. It is thus possible to prevent the fuel pump withdrawal port from getting aloof from the liquid level when the vehicle is suddenly accelerated or decelerated or when the vehicle runs along a slope.
With the above fuel feeder, however, it is necessary to use a jet pump to lead fuel in the fuel tank into the sub-tank, thus complicating the structure and increasing the cost. Usually, therefore, a fuel feeder is adopted, in which fuel in the fuel tank is led into the sub-tank without use of any jet pump.
FIG. 1 is a partly broken-away schematic perspective view showing a fuel tank of such a prior art fuel feeder.
The illustrated fuel tank has a fuel tank body 1, which accommodates a sub-tank 2 disposed on its bottom. The sub-tank 2 has a box-like shape open at the top. Around the sub-tank 2, a spiral or maze-like fuel passage 3 is provided to communicate the inside and outside of the sub-tank 2. With this arrangement, fuel contained in the tank body 1 is led into the sub-tank 2 due to a liquid level difference.
In the sub-tank 2, a fuel pump 4 is provided to pump out fuel into the engine. The pump 4 has its withdrawal port 5 also disposed in the sub-tank 2. The withdrawal port 5 is provided with a filter 6, which extends along the bottom of the sub-tank 2.
In the sub-tank 2 is also disposed a lower end outlet 8 of a return duct 7, through which excess fuel is returned from the engine to the sub-tank 2.
In the fuel feeder having this structure, fuel in the tank body 1 is led through the fuel passage 3 into the sub-tank 2. Fuel retained in the sub-tank 2 is withdrawn through the filter 6 and pumped out by the fuel pump 4. Excess fuel is returned from the engine through the return duct 7 into the sub-tank 2. As the liquid level in the sub-tank 2 is reduced by feeding fuel to the engine, fuel in the tank body 1 is led into the sub-tank 2 due to a liquid level difference that is produced. Thus, the liquid levels inside and outside the sub-tank 2 are held to be substantially equal.
When fuel in the tank body 1 is brought to one side thereof due to an exerted momentum or the like, a major portion of fuel in the sub-tank 2 is retained in the inside thereof. Thus, the possibility that the filter 6 provided on the withdrawal port 5 of the fuel pump 4 gets aloof from fuel is reduced to eliminate or alleviate the pressure reduction of fuel fed to the engine.
Meanwhile, blended fuel engines are recently considerably popular, which have an aim of low gasoline consumption and use blended fuel prepared by adding alcohol to gasoline. Such an engine requires an increased amount of fuel fed to it because the required consumption of 100% pure alcohol, for instance, is substantially double that of 100% pure gasoline. Therefore, if the above fuel feeder comprising the fuel tank provided with the sub-tank is to be used, it is necessary to accommodate a sufficiently increased amount of fuel in the sub-tank.
In the fuel feeder shown in FIG. 1, since fuel is led to the sub-tank 2 with the sole liquid level difference, if it is intended such that sufficient fuel is retained in the sub-tank 2 even when the liquid level in the fuel tank 1 is reduced, the sub-tank 2 should have a considerably large bottom area. However, by increasing the bottom area of the sub-tank 2, the following problem is posed.
FIG. 2 shows the case when the bottom area of the sub-tank 2 shown in FIG. 1 is increased.
While the vehicle is running normally, the filter 6 is held submerged in fuel even when the liquid level in the sub-tank 2 is reduced because the liquid level surface is held substantially horizontal. So far as this condition alone is concerned, increasing the bottom area of the sub-tank 2 leads to no problem. However, when fuel in the sub-tank 2 is brought to one side thereof due to sudden acceleration or deceleration or turning of the vehicle or running thereof along a slope, the liquid level surface is suddenly tilted, as shown in FIG. 2, resulting in a reduced contact area of the filter 6 with fuel. Therefore, the quantity of fuel withdrawn by the fuel pump 4 is reduced. This means that in spite of the provision of the sub-tank 2 the effective quantity of fuel fed to the engine is not substantially increased. That is, any benefits of the sub-tank 2 are substantially reduced.
It may be thought to increase the area of the filter 6. However, the filter area is limited by the withdrawal force of the fuel pump 4. Besides, even if the filter area is increased, an increase of the filter area exposed from the liquid level surface may result in air withdrawal. Therefore, increasing the filter area is not effective.